This study involves behavioral and physiological investigations of sound detection mechanisms in fishes. Primary emphasis is placed on behavioral determinations of auditory sensitivity in a variety of marine teleosts. These same species are being used in physiological studies of the inner ear for investigations of the detection capabilities and analysis mechanisms of the ear. Experiments involve recording of microphonic potentials and single-units of the 8th nerve. Particular attention is being placed upon determining the responses of auditory units innervating sensory hair cells that are morphologically oriented in different directions. Animals are being stimulated with both pressure stimuli and direct vibration as a mechanism for understanding directional responses of the ear. BIBLIOGRAPHIC REFERENCES: Popper, A. N. and Fay, R. R. (1977) The structure and function of the elasmobranch auditory system. American Zoologist, in press. Popper, A. N. (1977) A scanning electron microscopic study of the sacculus and lagena in fifteen species of teleost fishes. J. Morphol., in press.